Why home tests may need lab confirmation

If you've ever had a home result that surprised you, you'll know how quickly a single line on a plastic card can turn into a crisis. Laboratory confirmation exists for exactly that moment. It is the difference between "the screen reacted" and "we know what was in the sample."

Home tests are the first of two steps

The U.S. Food and Drug Administration (FDA) describes home drug testing as a two-step process. The home test is a quick first check. If it suggests a drug may be present, the sample goes to a laboratory for a more specific chemical test. FDA calls laboratory tests the most reliable way to confirm drugs of abuse, and its advice after a preliminary positive is plain: take no serious actions until you have the laboratory's result.

The same idea appears in the regulatory paperwork for individual products. In one FDA 510(k) decision summary for a home test (K050936), the intended use describes the kit as "only the first step in a two-step process". It also states that the screen gives only a preliminary result, that a more specific alternate chemical method must be used to confirm it, and that gas chromatography/mass spectrometry (GC/MS) is the preferred confirmatory method.

Why a screen can be wrong

A screening test is built to be quick and sensitive. FDA notes that a drug present in urine will usually produce a preliminary positive. But FDA also lists things that can affect home results:

• how the test was performed;
• how the test or the urine was stored;
• what the person ate or drank;
• prescription and over-the-counter medicines. FDA specifically flags that some over-the-counter medicines can produce the same result as amphetamines.

FDA also points out that a positive result for a prescription drug doesn't show misuse, because the test can't tell an acceptable level from an abusive one. A laboratory, and a healthcare professional who knows the person's medicines, are far better placed to make sense of that.

What about negative results?

Confirmation is usually discussed for positives, but negatives have limits too. FDA notes that no test of this type is 100% accurate, and that a negative can happen because the test didn't screen for the substance, the sample was collected outside the detection window, or the test had degraded through improper storage or age. If a real concern remains after a negative, FDA suggests testing again later and talking with a doctor.

The ways laboratory testing can happen

There are a few routes, and the right one depends on your situation. Check what's available where you live.

• A home kit with a mail-in option. Some home kits include materials for sending part of the sample to a lab. In the K050936 example, the kit included a collection cup with a confirmation label and shipping materials. For that product, the decision summary says the confirmation test was included in what the buyer paid for the kit, but the buyer paid separately to ship the sample. Other products differ, and not every kit includes this, so check before you buy.
• A home collection kit. FDA describes collection kits where you collect a sample at home and send it to a laboratory, which does the testing. FDA says the price of these kits usually pays for the analysis, and that the lab first screens the sample and, if the screen suggests a drug may be present, does a more complete analysis and reports the results to you. FDA describes laboratories as using a very reliable test with very few errors.
• Through a healthcare professional. A doctor can order testing and help interpret results in the context of a person's health and medicines.

The random scheduling and accountability service is free. Test kits and any laboratory testing are purchased separately. Laboratory confirmation is a real cost to plan for, and it's better to know what it involves before a difficult result than after.

Plan for confirmation before you need it

The calmest time to agree on confirmation is when everyone is getting along. Many people write a few lines like these into their agreement:

• A home result is a screening result. Nobody takes serious action on it alone.
• If a screen is presumptive positive, we follow the kit's instructions and arrange laboratory confirmation.
• We know in advance which route we'd use and roughly what it costs.
• We keep the kit's instructions until the result is settled.
• We talk about what happened only after the lab result is back, and we use neutral words.

That last point matters. The National Institute on Drug Abuse recommends neutral terms like "testing positive" and "testing negative", rather than "clean" or "dirty". See encouragement without shaming for more.

What an app can and can't do

P in the Cup is a free scheduling and accountability service whose app is launching soon. It does not sell, administer or interpret tests. A result someone reports in an app, or a photo of a test, is not a laboratory-verified result, and we'll never describe it as one.